| Summary: | We here reported the identification and characterization of a novel gain-of-function spotted-leaf 26 (Spl26) mutant from an ethylmethylsulfone (EMS)-induced rice cultivar IR64. Spl26 displayed reddish- brown lesions that firstly appeared on the leaf tips at the early tillering stage and spread gradually downward to cover the whole leaf blades that wilted subsequently. The lesion development was light- dependent under natural conditions. Spl26 exhibited impaired photosynthetic capacity with decreased chlorophyll content and lowered photosynthetic parameters which ultimately led to the poor performance of agronomic traits. Severe cell death occurred in Spl26 in accompany with increased malonaldehyde level and membrane ion leakage rate, elevated reactive oxygen species (ROS) accumulation, altered ROS scavenging activities, increased DNA fragmentation and decreased soluble protein levels. Defense responses were activated in Spl26 with enhanced resistance to rice bacterial blight, up-regulation of defense response genes and altered endogenous hormone levels. The spotted-leaf phenotype is controlled by a single dominant nuclear gene localized to a 305 kb region between RM5490 and InDel42 on the short arm of chromosome 7. The data suggested that Spl26 is a novel gain-of-function spotted-leaf mutant with enhanced bacterial disease resistance and immunity-associated premature leaf senescence and would provide the basis for cloning of the target gene. Keywords: Defense response, Rice, Reactive oxygen species, Senescence, Spotted-leaf, Disease resistance
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